The findings suggest older patients should not put off surgery because they're concerned that general anesthesia might affect their thinking and memory in the future, the researchers concluded.

The study included nearly 4,300 twins younger than 70 and about 4,200 twins aged 70 and older in Denmark who were given tests to assess their thinking and memory abilities.

The researchers compared twins who had various types of surgery between 18 and 24 years earlier with those who did not have surgery.

There was no significant link between major surgery, general anesthesia and long-term mental decline, according to the study published recently in the journal Anesthesiology.

"Our use of twins in the study provides a powerful approach to detect subtle effects of surgery and anesthesia on cognitive functioning by minimizing the risk that the true effects of surgery and anesthesia are mixed up with other environmental and genetic factors," lead author Unni Dokkedal, of the University of Southern Denmark, said in a journal news release.

"We found no significant cognitive [thinking] effects related to surgery and anesthesia in these patients," Dokkedal said. This suggests that other factors, such as preoperative mental decline and underlying diseases, are more important to mental functioning in aging patients following surgery.

The study adds to growing evidence that "older patients should today be reassured that surgery and anesthesia are unlikely to be implicated in causing persistent cognitive decline or incident dementia," Michael Avidan and Dr. Alex Evers, of Washington University School of Medicine in St. Louis, wrote in an accompanying editorial.